1. Field of the Invention
This invention relates to method and apparatus for cutting gas well casings in the explosive environment of an underground coal mine and more particularly to a cutting nozzle assembly for generating a three phase high velocity coherent stream of air and abrasive particles mixed with water for cutting metal pipe without generating sparks.
2. Description of the Prior Art
In underground mining operations it is not uncommon in dislodging a seam of coal to encounter a gas well casing that extends down to the coal seam. If the dislodging means of a mining machine, such as the cutting scroll of a longwall mining machine, should come in contact with the metal casing, the sparks that are generated and the associated heat could cause an explosion if there is the requisite concentration of methane gas in the working environment. In many instances the gas well pipe is charted on the mining maps but it is not uncommon to encounter an uncharted gas well casing. In such an instance the mining machine must be removed from the face before it contacts the casing and arrangements made to remove the casing in a safe manner.
Water jet cutting nozzles are well known in the art as disclosed in U.S. Pat. Nos. 4,545,157; 4,648,215; 4,478,368; 4,707,952 and 4,723,387. With each of these devices pressurized water and a stream of abrasive particles are introduced separately into the mixing chamber of a cutting nozzle. The high velocity jet of water comes in contact with the abrasive particles and momentum is transferred from the water to the particles to form a high velocity stream of abrasive particles entrapped within the stream of water that exits the cutting tip of the nozzle assembly. The abrasive water jet stream is then used in a variety of cutting operations, such as cutting rock, concrete, asphalt and metals such as reinforcing rod.
A problem that is encountered with the cutting of metal by water jet abrasives is the generation of sparks. In a hazardous environment, such as underground coal, the presence of methane in the atmosphere can create an explosion when sparks are generated by the action of cutting with abrasives even in a water jet slurry where the abrasive particles are relatively large.
While it is known to cut metal with abrasive particles encapsulated in a fluid jet stream, the known water jet cutting nozzles do not satisfactorily eliminate the hazard of sparking when cutting metal such as gas well casing in an underground mine.
Therefore, there is need for a fluid cutting machine that is adaptable for use in cutting metal in an underground mine and other similar hazardous environments where sparking is eliminated. The fluid cutting machine, when not in use to cut gas well casings in advance of the mine machine, should also be available to perform other cutting tasks, such as drilling bore holes in the mine roof for installation of mine roof support devices and for coal dislodging operations.